Traditional shaft sinking operations are carried out by drilling and blasting below a work stage, to excavate material from a hole, and removing the excavated material using a mucking system by which the excavated material is picked up and deposited in buckets or kibbles that are hoisted to the surface. More recently there have been proposals to increase the speed at which sinking can progress by using earth boring machinery. International patent publication number WO 2011/000037A1 discloses such a proposal for sinking a mineshaft in which earth excavated by a boring machine is transferred into large capacity conveyances in the form of skips or buckets that are raised and lowered by a hoisting system installed at the mine surface or at the top of a winze. On completion of shaft sinking operations the hoisting system and skips may subsequently be operated to convey material excavated during production mining.
As mentioned above, traditional shaft sinking uses buckets or kibbles in place of skips. This is because buckets and kibbles are open-topped to facilitate mucking, and to fulfil shaft bottom access requirements (e.g. where personnel are transported in the buckets). Once the buckets or kibbles descend below the work stage, they are unguided—in other words, the buckets or kibbles can rotate and swing laterally. Unguided movement is borne out of necessity, since any guides below the work stage would be blasted away by the next blasting operation at the bottom of the mineshaft.
Since the buckets or kibbles are able to rotate, they are generally round. The round shape ensures consistent accessibility for mucking, regardless of the orientation of the buckets or kibbles when they reach the bottom of the mineshaft. Moreover, buckets and kibbles are open-topped so that they are consistently open and available for loading, regardless of orientation. In contrast, skips generally have an enclosed top and load through an opening in the upper side, meaning they can generally only be loaded from a particular direction. Skips also generally discharge through the bottom, which is a discharge process that is incompatible with conventional shaft mucking and unloading equipment. Skips typically have a square cross-section and therefore cannot travel below the work stage for mucking since it is difficult to control the skips to ensure they are oriented correctly for mucking. Lastly, while buckets and kibble are detachable to allow multiple buckets or kibbles to be concurrently position on the bottom of the shaft, skips are permanently attached to the hoist rope. Skips are therefore not appropriate for use in blasting and mucking operations.
In all cases where a conveyance travels up a shaft, above personnel or crews, it is desirable that the conveyance be brought to a halt, in the event that it experiences any uncontrolled movement. Some systems for responding to uncontrolled movements provide hoist motor controls that cease hoisting the conveyance when, for example, an overwind event occurs (i.e. the conveyance travels past its discharge position in the head frame). However, ceasing to hoist the conveyance does not necessarily prevent against subsequent freefall of the conveyance, particularly in the case that the hoist rope breaks.
Although the system of the present disclosure has arisen from the desire to provide safeguards when hoisting heavily loaded skip conveyances, particularly where those conveyances travel above crews (e.g. are suspended loads above personnel), it may be applied to the hoisting of any mineshaft conveyance where protection against uncontrolled movements of conveyances in desirable.
The term “skip” refers inter alia to a conveyance used to bring mined material to the surface of a mine shaft. Skips are manufactured in various sizes and designs for both vertical and incline shafts, including closed-topper tip over models and bottom door dump models
Skips are distinct from “buckets” insofar as:                a) skips are self dumping (whether tip over i.e. from top or bottom);        b) skips are utilised in production shafts (not in construction/sinking);        c) skips are permanently attached to the hoist rope; and        d) skips do not have to be able to stand on the bottom of a mineshaft (i.e. can be extremely long and slender)        
A “bucket” and “kibble” are each a cylindrical shaped conveyance, use to transport blasted muck from the shaft bottom, during sinking operations.
When compared with skips, buckets:                a) require manual dumping        b) must be unloaded in a tip over fashion        c) are attached to the hoist rope via detachable hook to suspension chains (or bale) at the top of the bucket (minimum of 3 to maintain stability)        d) must be used in conjunction with a crosshead to provide guidance in the shaft barrel        e) are unguided below shaft guide system or work stage        f) must be used with only low spin or lock coil hoisting ropes        g) are regularly removed from the hoist rope (generally to load at shaft bottom) during the loading operation        h) must be round and have a height to diameter ratio that is stable and will stand unsupported on shaft bottom.        
Unless context specifies otherwise, the term “guide” as used herein refers to a member along which a conveyance travels down a mineshaft, and that resists or prevents rotation of the conveyance and lateral movements of the conveyance relative to the mineshaft. Such a “guide” provides no motive or drive force to cause movement of the conveyance.